1. Field of the Invention
The present invention relates to a slurry composition, and a green sheet, for barrier ribs of plasma display panel, particularly to a slurry composition, and a green sheet, for double-layered barrier ribs. The present invention also relates to a method for manufacturing a double-layered barrier rib.
2. Description of the Related Art
A plasma display panel (PDP) is a flat panel display device that can display images or information by using the light-emitting phenomenon of plasma discharge. Generally, PDPs are divided into DC-types and AC-types according to panel structure and driving method.
PDPs are display devices using the light-emitting phenomenon of visible photons generated from the energy difference occurring when ultraviolet radiation excites a phosphor lining in a cell and then returns to the ground state, wherein the ultraviolet radiation is generated by discharge of a gas (such as He, Xe, etc.) provided in each cell when generating plasma discharge in a discharge cell divided by ribs.
PDPs have such advantages as easiness in manufacturing by simple structure, high brightness, high luminous efficacy, memory capacity, and wide viewing angle over 160°. PDPs can also be advantageously used for wide screens of 40 inches or more.
Hereinafter, the basic structure of a PDP will be described.
The structure of a PDP generally includes an upper substrate and a lower substrate oppositely disposed thereto, barrier ribs, and cells defined by the two substrates and barrier ribs. Transparent electrodes are disposed on the upper substrate, and bus electrodes are disposed on the transparent electrodes in order to reduce resistance of the transparent electrodes. Address electrodes, also called data electrodes, are formed on the lower substrate.
The cells divided by the barrier ribs are lined with phosphors. Further, an upper dielectric layer is disposed on the upper substrate to cover the transparent electrodes and the bus electrodes. Also, a lower dielectric layer is disposed on the lower substrate to cover the address electrodes. A protection layer, generally consisting of magnesium oxide, is disposed on the upper dielectric layer.
The barrier ribs are present to maintain a discharge distance between the upper substrate and the lower substrate, as well as to prevent electrical, optical cross-talk between adjacent cells. Formation of the barrier ribs is one of the most important steps in the manufacturing process of PDPs in order to achieve good display quality and efficiency. Therefore, there has been much research on the formation of barrier ribs, as the size of panels increase.
In general, the barrier ribs are formed by the Sand Blasting method, the Screen Printing method, or the Photo Etching method.
In the Sand Blasting method, the address electrodes and the dielectric layer are first formed on the lower substrate, and then a glass paste, used as the material for the barrier ribs, is applied thereto, followed by a sintering step. Next, a stripe type of mask pattern is disposed thereon, and fine sand particles are sprayed thereon at high speed through the mask pattern, thereby forming the barrier ribs.
In the Sand Blasting method, the cost of equipment is high, and the process is also complex. Moreover, a considerably high physical impact is applied to the lower substrate, and thus, cracks may be caused during the sintering step.
In the Screen Printing method, the address electrodes and the dielectric layer are formed on the lower substrate, followed by disposing a stripe type of screen thereon. Subsequently, printing is performed repeatedly with a glass paste, used as the material for the barrier ribs, until a desired thickness of barrier ribs is obtained. Then, sintering is performed thereto.
In the Screen Printing method, the number of screen-printing steps is increased to obtain a desired thickness of barrier ribs due to limitations in the height of barrier rib which can be obtained by one screen-printing step. And, by repetition of the screen-printing step including aligning of the screen and the lower substrate, printing, and drying, the process becomes complex.
In the Photo-etching method, the address electrodes and the dielectric layer are first formed on the lower substrate, and then a paste, used as the material for the barrier ribs, is applied thereto. Then, a stripe type of mask pattern is positioned, and then the barrier ribs are shaped by etching the exposed portions through openings of the mask with an etching agent. This is then followed by sintering.
In the Photo-etching method, the process is delayed because the paste is applied several times to create the desired thickness of barrier ribs. Also, it is difficult to obtain barrier ribs that are shaped structurally and mechanically stable enough to retain the discharging space because the side portions are over-etched.
In short, conventional methods for forming the barrier ribs are complex as well as time-consuming, thus, the manufacturing costs are high. Further, it is difficult to form the barrier ribs to a desired shape with conventional methods.
For the foregoing reasons, there has been a need to develop an invention that can manufacture barrier ribs cheap, simply, and with a desired shape.